S&P 500: The Winners and Losers of May 2025
The S&P 500’s journey through early 2025 has been marked by dramatic volatility and a remarkable recovery. After opening the year with a solid 2.7% gain in January, the benchmark index faced headwinds through February and March, declining 1.4% and 5.75% respectively. April proved particularly turbulent, with sharp market swings partly triggered by new tariff policies from the current administration. The index plunged to a low of 4,835 on April 7 before staging a gradual comeback, ultimately closing the month down just 0.76%.
May delivered the year’s strongest performance, with the S&P 500 surging 6.15% and climbing back toward record highs. The broad-based rally was evident across the index, with 346 of the 500 constituents posting positive returns while 154 stocks declined.
In this article, we break down the top-performing and worst-performing S&P 500 stocks in May 2025 and explore the key news and developments that influenced their movements.
Top S&P 500 Performers in May
Among the top performers were NRG Energy ($NRG), Constellation Energy ($CEG), and Seagate Technology ($STX). Here’s a closer look at what drove each stock’s strong May rally.
NRG Energy ($NRG) +42.27%
NRG Energy surged over 42% in May, making it the top-performing S&P 500 stock for the month. The rally was fueled by a combination of strong earnings and a major acquisition announcement.
The company posted first-quarter adjusted earnings of $2.62 per share, far exceeding analyst expectations, and reported $8.59 billion in revenue. Investors cheered the news of a $6.4 billion deal to acquire LS Power’s “Premier Power” portfolio, which will double NRG’s power generation capacity and add a 6 GW virtual power plant business.
This acquisition, paired with NRG’s reaffirmed 2025 outlook and planned $1.3 billion in shareholder returns, boosted investor confidence. Broader sector trends—notably a rebound in energy stocks—further supported the stock’s strong performance.
Constellation Energy ($CEG) +37.02%
Constellation Energy rose 37% in May, driven by strong quarterly earnings and strategic positioning in the clean energy transition.
The company reported Q1 adjusted earnings of $2.14 per share, an 18% year-over-year increase, and maintained its full-year guidance. Additionally, ongoing progress on its $16.4 billion acquisition of Calpine Corp reassured investors about its future growth prospects.
Broader nuclear energy tailwinds also played a role. The Trump administration issued executive orders in May aimed at accelerating a “nuclear energy renaissance,” further increasing investor optimism about the sector’s future and Constellation’s leadership position.
Strategic grid and AI-related developments added to the momentum. PJM, a major grid operator, fast-tracked the interconnection of Constellation’s Crane Clean Energy Center, supporting the restart of a dormant nuclear plant to meet the energy needs of Microsoft’s AI infrastructure. These actions highlight Constellation’s growing role as a key supplier of reliable, carbon-free power to technology giants, a theme that has resonated strongly with investors amid the AI boom.
Seagate Technology ($STX) +29.56%
Seagate Technology, a provider of data storage solutions for enterprises and cloud infrastructure, advanced nearly 30% in May, benefiting from strong earnings and renewed optimism around AI-driven storage demand.
The company exceeded fiscal Q3 expectations with earnings of $1.90 per share on $2.16 billion in revenue, up 30% year-over-year. Growth was driven by surging demand for high-capacity storage from cloud providers and AI data centers.
Seagate further boosted investor confidence by announcing a $5 billion share buyback program, signaling management’s belief in the company’s intrinsic value and future prospects. Meanwhile, Seagate’s investor event highlighted advancements in next-generation drive technologies, particularly in Heat-Assisted Magnetic Recording (HAMR), reinforcing its technological leadership and positioning the company as a key player in the AI and cloud storage ecosystem.
Worst S&P 500 Performers in May
Among the worst performers were UnitedHealth Group ($UNH), Regeneron Pharmaceuticals ($REGN), and Eli Lilly and Co ($LLY). These stocks struggled due to company-specific challenges and sector pressures.
UnitedHealth Group ($UNH) –26.62%
UnitedHealth Group, one of the largest health insurance and healthcare services providers in the U.S., fell 27% in May amid a series of major challenges.
The company’s Q1 results showed a sharp increase in healthcare utilization, especially among seniors on Medicare Advantage plans, which led to a rare earnings miss and a significant reduction in its 2025 EPS forecast, from $29.50–$30.00 to $26.00–$26.50. Management cited rising medical costs and reimbursement shortfalls, particularly in its Optum division.
Investor sentiment deteriorated further with the unexpected resignation of CEO Andrew Witty on May 13, citing “personal reasons.” His departure followed the earlier tragedy of UnitedHealthcare CEO Brian Thompson’s death in late 2024, adding to the leadership instability. Stephen Hemsley, UnitedHealth’s longtime chairman and former CEO, was reappointed as CEO during the transition.
Compounding the turmoil, UnitedHealth also withdrew its full-year 2025 guidance and, on May 14, reports emerged that the company is under a U.S. Department of Justice criminal investigation regarding possible Medicare fraud linked to overbilling practices in Medicare Advantage.
These combined factors—earnings misses, leadership upheaval, legal scrutiny, and suspended guidance—eroded investor confidence and sent UnitedHealth shares to four-year lows.
Regeneron Pharmaceuticals ($REGN) –18.12%
Regeneron’s stock declined 18% in May after disappointing results from its Phase III COPD drug trials.
The company’s experimental therapy, itepekimab, yielded mixed results—success in one trial but failure in another—casting doubt on the drug’s regulatory prospects and future revenue potential. The market reacted sharply, with shares plunging nearly 19% in a single day following the announcement.
Broader biotech sector underperformance also weighed on Regeneron, but the primary driver of its decline was the uncertainty surrounding a key growth catalyst.
Eli Lilly and Co ($LLY) –17.94%
Eli Lilly fell nearly 18% in May, pressured by high expectations and rising competitive concerns in the obesity drug market.
Despite strong Q1 results, the company trimmed its full-year earnings guidance due to a one-time acquisition-related charge. Additionally, CVS Health’s decision to exclude Lilly’s Zepbound from its preferred formulary in favor of Novo Nordisk’s Wegovy stoked fears of market share erosion.
The news triggered a sharp selloff, with shares dropping more than 11% in a single session and continuing to slide throughout the month. Investors reassessed Lilly’s growth trajectory, leading to one of the steepest declines among large-cap pharmaceutical stocks in May.
This article is for informational purposes only and is not investment advice or a solicitation to buy or sell securities. The content is based on publicly available information and reflects the author’s opinions as of the publication date, which may change without notice. All investments carry inherent risks, including the potential loss of principal, and past performance is not indicative of future results. Readers should conduct their own research or consult a financial advisor before making investment decisions. BBAE holds no position in the securities mentioned, nor are they compensated by the companies mentioned.
